Grieve ovens, also referred to as furnaces, are utilized to process materials at elevated temperatures for homogenization, recrystallization, die pressing, annealing, stress relief, and hot rolling. These heat treatment processes provide methods of controlling grain structures, grain sizes, distributions of alloying elements, and grain orientations. Desirable sizes and shapes are obtained by rolling after the heat treatments. Manual operations are employed to control all heat treatment processes. Operators set the cycle temperature at the setpoint, or the "aim temperature," of the temperature controller 30. When the oven is heated to a temperature close to the cycle temperature, materials are loaded in the oven for heat treatment. Heat treatment time begins to count once the oven door is closed.
This manual process has many disadvantages, which leads to improperly heat treated materials and thus waste or defective products.
Exposure time to the cycle temperature might not be consistently controlled. This can be due to the operator failing to initiate the timer properly or to remove the material promptly when cycle time has expired. Since recipe parameters are manually referenced, the operator may reference the cycle time incorrectly.
Variations in temperature control occur since process control is subject to the discretion of individual operator. Mistakes happen for many reasons, such as when the operator incorrectly references the appropriate heat treatment recipe. A different operator assumes control of an ongoing treatment at shift change and may make a mistake as to the temperature parameters. The operator may take more or less than time than average in loading the material, allowing the starting temperature to vary from the expected temperature due to the door being open. Undetected degraded hardware could cause loss of control over the cycle temperature.
This lack of real-time monitoring creates additional disadvantages of the manual system. The lack of an automatic alert wastes time causing an economic loss. Relying on an individual operator to monitor the process closely causes increased labor expense in staffing and training. Moreover, the mundane nature of such manual monitoring makes timely detection difficult.
Improvements using statistical process control are difficult to accomplish since historical temperature data is not automatically gathered. As is the real-time data, the historical data is subject to the errors during manual collection. Moreover, errors are introduced when inputting the manually-collected data for analyzing for statistical process control (SPC) purposes. These additional steps make the time delay and frequency in such calculations problematic.
Therefore, a significant need continues to exist for a manner of controlling heat treatment furnaces to reduce amount of improperly processed materials and to reduce the labor expense.